This invention relates to communication systems and, more particularly, to a pulse duration multiplexing communication system. In my earlier U.S. Pat. No. 4,345,323, the disclosure of which is hereby incorporated by reference herein, I disclose a system and a method for the multiplexing of digital data to enable simultaneous transmission/reception of a number of digital signals over a single communication channel. A plurality of input signals are clocked in and assigned respective binary coded weighted values. The combined binary coded weighted value of the input signals determines the time duration of a digital data pulse which is generated by the system. The multiplexed data is thereby represented by the length, or duration, of the generated pulse. This data pulse is then transmitted to a receiver, where it is amplified and quantized to a digital level and output signals are generated in correspondence to the digital transmitter input signals.
In a system of the type disclosed in the referenced patent, if a low tolerance, high accuracy, clock pulse generator, such as a crystal oscillator, is used at both the transmitter and the receiver, there is no problem with encoding and decoding the pulse durations. However, if the clock pulse generators at the transmitter and at the receiver operate at different frequencies, errors in decoding received pulses can occur. In a system of the type disclosed in U.S. Pat. No. 4,682,168, where there is a relatively complex central unit, or system controller, along with a plurality of relatively simple remote units, all interconnected via a data bus and clock bus, it may be economically feasible to utilize a precise crystal oscillator as part of the clock pulse generator in the central unit. However, the circuitry within each of the remote units is preferably incorporated within an application specific integrated circuit (ASIC), and the use of a crystal oscillator in conjunction therewith is inconvenient and not cost effective. Unfortunately, oscillators available in an ASIC are not very accurate. Therefore, the transmitter and receiver may not be operating at the same frequency.
Accordingly, it is a primary object of this invention to provide a pulse duration multiplexing system and a method for use therein which provides reliable signal decoding even with the use of clock pulse generators having a relatively large tolerance in their accuracy without the need for a clock bus.